1. Technical field of the Invention
This invention relates generally to electroacoustic transducers and, more particularly, to an electroacoustic transducer including loudspeakers employing a diaphragm substantially of a dome shape having an irregular sectional shape.
2. Related Art
The electroacoustic transducers employ the diaphragm of various types including a cone shape, planar shape and so on as adapted to reproduced sound of bass, middle and so on, in which there has been a dome-shaped diaphragm designed specifically for reproducing a high range of audio frequency.
Referring to an example of a known electroacoustic transducer such as a loudspeaker unit utilizing the dome-shaped diaphragm, this diaphragm is circular in its plan view and semicircular in a side view and is thus formed to be hemispheric as a whole, the hemispherical diaphragm is supported at outer peripheral part through an edge member onto a magnetic circuit, and a voice coil is wound on outer periphery at one end part of a cylindrical voice-coil bobbin coupled at the other end to the outer peripheral part of the diaphragm, and the voice coil is positioned in a gap of the magnetic circuit so that the diaphragm can vibrate in response to voice signals provided to the coil for radiating sounds. The magnetic circuit comprises a yoke having a center pole, an annular permanent magnet placed around the center pole, and an annular top plate placed on the magnet to define the gap between the inner periphery of the top plate and the outer periphery of the center pole.
 less than Problem to be Solved by the Invention greater than 
This dome-shaped, hemispherical diaphragm is in axial symmetry in which the distance between an apex of the dome shape and all circumferential positions at the outer periphery along which the voice coil bobbin is coupled is equal all over the circumferential positions, and the vibration transmitted from the voice coil to the outer periphery of the diaphragm is caused to concentrate at the apex in equiphase so that resonance is apt to occur in the mode of axial symmetry so as to cause the frequency characteristic curve to involve remarkable peak dips specifically in the higher range of the audio frequency, whereby it has been made unable to attain an excellent tone quality.
Attempts have been suggested to remove such problem of the axially symmetrical mode of the resonance, in some of which suggestions the dome-shaped diaphragm has been made irregular in the section for inducing axially asymmetrical mode of resonance. For example, in JP-A 50-39925 of Apr. 12, 1975, it is suggested to form the diaphragm substantially in a dome shape but having different distances between a top central portion and all circumferential positions at the outer peripheral driving end. In JP-A 55-71394 of May 29, 1980, further, the dome-shaped diaphragm is suggested to be formed to have an axially asymmetric top projection. With these attempts, however, the shape possible in the suggested formation should vary in a rather wide range so as to be difficult to determine definitely any practically effective shape, and the effect of these suggestions is still uncertain and not reliable in respect of intended removal of the peak dips in the higher frequency range.
The present invention has been suggested in view of the foregoing and its object is to provide an electroacoustic transducer employing a substantially dome-shaped diaphragm for the electroacoustic transducers capable of attaining the excellent tone quality.
 less than Measures for Solving the Problem greater than 
The present invention establishes the above object by providing an electroacoustic transducer comprising a diaphragm formed substantially in a dome shape having a circular outer periphery and caused to vibrate in response to one of an external acoustic energy and an internal electric energy, and an electric system including a voice coil coupled to the diaphragm to vibrate together therewith for one of conversion of vibrations of the diaphragm responsive to the acoustic energy into corresponding electric signals and of electric signals corresponding to sounds to be reproduced into acoustic energy through the vibration of the diaphragm; the dome shape of the diaphragm including a central arcuate ridge line of a first radius of curvature across the circular outer periphery and passing through an apex of the dome shape, and surfaces formed on both sides of the central ridge line respectively with side sectional line intersecting at right angles with the central ridge line and having a second radius of curvature larger than the first radius of curvature of the central edge line.
The present invention further provides, for attaining the foregoing object, a loudspeaker comprising a magnetic circuit including a yoke having a center pole and a peripheral plate, an annular magnet placed on the peripheral plate of the yoke, and a top plate placed on the magnet to form a gap between an inner periphery of the top plate and an outer periphery of the center pole, and a diaphragm assembly including at least a diaphragm of a dome shape having a circular outer periphery, a cylindrical voice-coil bobbin coupled to the diaphragm and carrying a voice coil on outer periphery of the bobbin, and an annular edge coupled at inner periphery to the diaphragm and secured stationary at outer peripheral part; wherein the dome shape of the diaphragm includes a central arcuate ridge line of a radius of curvature diametrally across the circular outer periphery and passing through an apex of the dome shape, and surfaces formed on both sides or the central ridge line respectively with side sectional lines intersecting at right angles the central ridge line and having a radius of curvature larger than that of the central edge line.
In the diaphragm employed either in the transducer or loudspeaker according to the present invention, the second radius of curvature of the side sectional lines of one of both side surfaces and/or of the other side surface is constant.
In the diaphragm of the present invention, further, the second radius of curvature of the side edge lines in one of both side surfaces is equal to that of the side edge lines in the other side surface.